Method of making shroud structures



April 1944- H. P. DAHLSTRAND 2,345,918

METHOD OF MAKING SHROUD STRUCTURE Filed May 14, 1941 Patented Apr. 4,1944 METHOD OF MAKING SHROUD STRUCTURES Hans P. Dahlstrand, Wauwatosa,Wis., assignor to Allis-Chalmers Manufacturing Company,

Milwaukee, Wis;

a corporation of Delaware Application May 14, 1941, Serial No. 393,317

2 Claims.

This invention relates generally to elastic fluid turbine blading' andmore particularly to a shroud construction for turbine blades; thestructural features of which have been made the subject of a divisionalapplication, Serial No. 430,855, filed February 14, 1942.

The construction most commonly employed heretofore comprised formingtenons at the ends of the blades which were passed through or insertedinto the holes in the shroud and either riveted over at their protrudingends or united with the shroud by a brazing or welding operation. Insome instances, the shroud has been deformed or recessed to providepositioning projections in the manner shown by U. S. patent to C. E.Search, No. 1,187,450, June 13, 1916, Steam turbine, and the topsurfaces of the blades were united with the bottom surface of the shroudby brazing. However, these known constructions have not been entirelysatisfactory since considerable stock is wasted in machining orotherwise forming tenons on the ends of the blades and since the tenonforming operation is time consuming and costly. Moreover, the rivetingor the welding of the tenon to the shroud produces a rough upper surfacewhich materially increases windage losses. Furthermore, it is extremelydifiicult and in many instances impossible to perform the tenon formingand riveting operations on blades which are mounted in a turbine andconsequently blades in actual service which require reshrouding usuallymust be removed from the.turbine which is a time consuming and a costlyprocedure. In addition, the removal of an existing shroud structurewhich is secured to the blades by riveting, brazing or welding requiresa cutting or grinding operation which invariably destroys the tenons andnecessitates the formation of new tenons, thereby reducing the effectivelength of the blades and the fiow capacity of the blading. The C. E.Search type of construction, which eliminates the tenon formingoperation, is also objectionable in that the upper surface is renderedrelatively rough by the formation of the positioning projections whichmaterially increases windage losses and in that the shroud strip must bebrazed to the ends of the blades before the blades are inserted in theturbine as it is commercially impractical to insert the entire turbinespindle in a brazing furnace. With the Search type of construction,blades in actual service which require reshrouding must also be removedfrom the turbine and consequently, the Search type of construction isalso objectionable and aifords but little actual changing the flowcapacity of the blading.

Another object of this invention is to provide an improved method ofshrouding the ends of turbine blades which entirely eliminates providingthe end of the blade which is to be shrouded with tenons, projectionsand the like for positioning and securing the shroud thereon.

Still another object of this invention is to provide an improved methodof shrouding the ends of turbine blades which produces a substantiallysmooth upper surface, thereby reducing windage losses.

Still another object of this invention is to provide an improved methodof shrouding the ends of turbine blades which is inexpensive and whichprovides a stronger construction than that heretofore produced by knownmethods.

The invention accordingly consists of the various methods and of thevarious details of construction, combinations of elements andarrangements of parts, as more particularly set forth in the appendedclaims and in th detailed description, in which:

Fig. 1 is a plan view of shrouding embodying the invention; 1

Fig. 2 is a sectional view taken on line II-II of Fig. 1;

Fig. 3 is a bottom view of the shroud shown in Fig. 1;

Fig. 4 is a plan view of the shroud as positioned on blading preparatoryto performing the welding operation;

Fig. 5 is a sectional view similar to Fig. 2 showing the shroudpositioned in superposed relation with respect to the end of a blade;

Fig. 6 is a sectional of Fig. 5;

Fig. 7 is a sectional view showing the shroud positioned on the end ofthe blade;

Fig. 8 is a sectional view taken on line VIII-VIII of Fig. 7;

Fig. 9 is a sectional view similar to Fig. 7 showing the structure afterthe weld metal has been deposited; and

Fig. 10 is a sectional view taken on line XX of Fig. 9.

Referring to the drawing and particularly Figs. 1-3, it is seen that theshroud I comprises view taken on line VI-VI depression of the side 2 asuitable metal stri having a base portion 2 dimensioned to span the endsof one or more blades and an upstanding sealing flange 3. The

base portion 2 'is provided with elongated openings 4 conforming innumber and arrangement to the ends of the blades on which the strip isto be positioned and secured. The length of each the blade at the end atwhich the shroud is to be attached and each opening is shaped tovapproximate theconfiguration of an intermediate and major portion of thesingle surfaced end of a blade as it appears when viewed in plan,v as isbest shown in Fig. 4. Statedfdiflerently, the side edges 6 and I of eachopening are shaped to conform with the portions of the side surfaces ofthe end of the blade which extend between points near the inlet andoutlet edges of the blade. The expression, single. surfaced end, as usedherein, is intended to apply to a blade end which is free of anyprojection or recess abruptly interrupting the continuity of the endsurface of the blade and therefore the expression includes blade endshaving surfaces which are either plane or curved, these surfaces beingeither perpendicular or oblique relative to the edges and to the sidesurfaces of the blade.

Each opening 4 has its opposite side edges 6 4 is somewhat less than thewidth of 10 and I forced downward a sufficient distance to providespaced opposed surfaces 8 and 9, respectively, adapted to receivetherebetween an intermediate and major portion of the single surfacedand of the blade to which the shroud is to be secured, as is best seenin Figs. 2-8, inclusive. Best results are obtained when, the distance towhich the side edges of the openings are depressed approximately equalsthe thickness of the metal shroud strip. The openings 4 and the edgesthereof may be formed in either one or two operations by using asuitable die or dies, respectively. However, the particular manner inwhich the openings [are made is immaterial and a furtherdescription inthis connection is not necessary for a complete understanding of theinvention.

The shroud strip containing the opening 4 is then placed on the singlesurfaced end of the blade ll so that portions of the underside of thebase 2. of vthe shroud strip adjacent each end of the opening 4 rests onor engages portions of the single surfaced end' of the blade adjacent,

the inlet and outlet edges thereof with the intermediate and majorportion of the single surassume space. provided between said surfacesand to fuse with said surfaces as indicated in Fig. 10. However,satisfactory results will be obtained if the surfaces 8 and 9 actuallyengage the side surfaces of the blade I i. After the shroud strip hasbeen weldedto the single surfaced end of the blade in the manner justdescribed, the resulting blade structure is preferably heat treatedinorder to remove any stresses which may have been set up incidental tothe welding operation.

The invention is applicable for reshrouding k existing'blade structureswithout removing the blades from the turbine and without changing theflow capacity of the blading, simply by removing the attached shroudstrip and the portions of the blades extendin above the under surface ofthe shroud strip, so as to provide the blades which are to be reshroudedwith single surfaced ends. The removal of the existing shroud structurefrom the blades can be readily accomplished by a suitable turning orgrinding operation .and preferably the, latter, since a portable handgrinding tool can be used. A shroud strip provided with the requisitenumber of openings 5 is then placed on the single surfaced ends of theblades and welded thereto in the manner hereinabove described. In thisconnection, a shroud strip dimensioned to span a series of severalblades should be welded first to one end blade of said series, then tothe other end blade of said series, then to a blade disposedapproximately midway between said end blades, and then to the remainingblades of said series in any desired order. This sequence of welding hasbeen found to produce a unitary structure which is suificiently freefrom welding stresses to permit the elimination of the stress relievingincrease in flow capacity and efficiency is attributable to the factthat the effective length of the blades remained the same while the sizeof the fillet on the underside of the replacement faced end-of thebladeconfined between the opposed surfaces 8 and 9 of' the depressed edgeportions 6 and I, respectively, as is best seen in Figs. 4, '7 and 8.The shroud strip l is held on the single surfaced end of the blade ii inthe position just described by any suitable means such as a clamp (notshown), and weld metal is deposited in the recess defined by thedepressed edges 6 and I and the portion of the single surfaced end ofthe blade which is confined between the surfaces Band 9. The weld metalI! may be deposited in the said recess by c any suitable means such asan electric arc welding apparatus (not shown), and sufficient metalshould be deposited to completely fill the recess,

, as shown in Figs. 9 and 10, thereby providing a shroud stripwasactually less than the cdrresponding fillet which was present on theoriginal structure.

The shrouding and reshrouding of blades in the manner herein describedis relatively inexpensive and provides a structure which is extremelydurable and considerably stronger than that heretofore produced by knownmethods and it should therefore be understood that is not desired tolimit the invention to the exact procedure and construction herein shownand described, as various modifications within the scope of the appendedclaims may occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. A method of shrouding a turbine blade shaped to present a singlesurfaced endwhich comprises providing a shroud strip having a,substantially plain fiuid confining surface, forming therein anelongated opening which is nearly as long as the distance between theinlet and outlet edges of the blade at the single surfaced end thereofdepressing the opposite side edges of said opening a distanceapproximately equal to the thickness of the shroud strip to form spacedopposed portions projecting inward from the plain surface thereof andshaped to conform with the configuration of an intermediate and majorportion of said single surfaced end of the blade as it appears in a planview thereof, placing the shroud strip on the single surfaced end of theblade so that portions of the under side of said strip adjacent the endsof said openin engage portions of said end of the blade adjacent theinlet and outlet edges thereof with the major portion of said endextending between and terminating substantially flush with the proximatesurface portions of said depressed side edges thereby forming anelongated recess having as its bottom surface the major portion of thesaid end of the blade, and uniting the shroud to the blade by depositingweld metal in said recess to substantially fill the same.

2. A method of shrouding a series of turbine blades shaped to presentsingle surfaced ends which comprises providing a shroud strip having asubstantially plain fluid confining surface, forming thereina series ofelongated openings conforming in number and arrangement to the singlesurfaced ends of the blades in said series and of which the length ofeach opening is somewhat less than the distance between the inlet andoutlet edges of the blades at the single surfaced end thereof,depressing the opposite side edges of each of said openings a distanceapproximately equal to the thickness of the shroud strip to form spacedopposed portions projecting inward from the plain surface thereof andshaped to conform with the configuration of an intermediate and majorportion of the end of the blade as it appears in a plan view thereof,placing the shroud strip on the single surfaced ends of the blades insaid series so that portions of the underside of the shroud stripadjacent the ends of each of said openings engage portions of the end ofthe underlying blade adjacent the inlet and outlet edges thereof with anintermediate and major portion of the end of each blade extendingbetween and terminating substantially flush with the outer surfaces ofsaid depressed side edges 'of the coacting opening to form acorresponding series of recesses each having as its bottom surface themajor portion of the said end of one of said blades, and uniting theshroud to the blades by depositing weld metal in said recess tosubstantially fill same.

HANS P. DAHLSTRAND.

